Exemplary embodiments of the present invention relate to weapons technology, particularly to an airborne laser weapon system that uses lasers pumped via optical waveguides.
Despite advances in aircraft design, conducting airborne reconnaissance or combat operations, especially at great distances from a home base, at great elevations or over extended periods of time, presents a challenge, a level of inconvenience due to the physical restrictions associated with such operations, and substantial risk to humans. This is particularly the case when the operation is itself associated with substantial hazards, e.g. it will be conducted in areas subject to enemy threats (“antiaircraft”), even up to the extreme case of a missile weapon system that is designed to deliver a warhead to a target and to self-destruct during the course of the mission. Naturally, the willingness of people to carry out such missions is somewhat limited.
In light of the above, efforts have long been underway to devise so-called unmanned aerial vehicles capable of performing such operations partially autonomously, partially remotely controlled from a base station and/or a transport means, but in any case without a crew.
Unmanned aerial vehicles (UAV) are currently known in multiple embodiments. For instance, some UAVs are designed for reconnaissance, i.e., the main purpose of such vehicles is to collect data about a situation/environment when this cannot be performed or can be performed only with difficulty from a distance, e.g. due to poor visibility or an inadequate overview of the situation. Also known are UAVs designed for warfare use, i.e. the main purpose of such vehicles is to destroy an object by delivering/administering one or more weapon systems that are carried on an aerial vehicle. (Guided) missiles represent a special embodiment of UAVs, with hybrid forms of said embodiments also being known.
Despite the extensive automation of such UAVs through advances in sensor technology, signals processing and decision making processes based on algorithms, there are still a large number of operations in which human powers of judgment cannot and should not omitted. Since a UAV carries no crew for performing such tasks, they must be performed by operators who are located, e.g., on the transport means, but in any case in a different location. To enable such operators to reach decisions and to influence the operation, data must be exchanged between the aerial vehicle and the operating unit provided for controlling the vehicle. These data are generally sensor data collected at the vehicle site/by the vehicle, which are intended to enable operators to assess the status and the situation, and control data, which are intended to enable operators to control the current and/or future behavior of the UAV, in the simplest case to guide the UAV, i.e., to influence its direction of travel in space.
Various technologies may be used for data exchange, e.g. electromagnetic radio waves in the decameter to decimeter wavelength range, which propagate in the atmosphere. However, these may be detectable and, in particular, susceptible to jamming/interference, and may have a limited range and/or a limited data rate. Also possible are electromagnetic waves in the decimeter to millimeter wavelength range; however, these are practicable only with a line of sight connection between transmitter and receiver. Another option is (laser) light propagating through the atmosphere, which is subject to essentially the same limitations as electromagnetic waves. A further option is electrical signals transmitted via lines, which may also involve risk due to the conductive connection, e.g. via high-voltage towers. Particularly preferable in the scope of the invention are optical signals transmitted via optical waveguides (“optical fiber guided”), the range of which may be limited to a certain extent, but may be greater than that of electrical lines. In this case, the exchange of data via optical waveguides can be a viable compromise that will allow particularly airborne weapon systems to be equipped with such data transmission systems. In particular, it is also possible for an airborne platform, e.g. a guided missile, flying at high speed, to tow an optical waveguide over great distances, e.g. several tens of kilometers, without the waveguide becoming detached or the transmission breaking down.
It is further possible in the field of optical waveguides (OWG), particularly optical waveguides with low damping, for large volumes of data to be reliably transmitted over many kilometers via the duplex method, so-called optical telecommunication, while at the same time transmitting high optical radiant power in the multi-kilowatt range from an optical source to a point located offset therefrom.
Applications of this type for such high-powered optical waveguides are known in the field of fiber-guided material processing systems, wherein the customary transmission paths lie within the range of several meters. The limiting factor for these transmission paths—aside from the requirements of the application—is the range of changes in beam properties that have a negative impact on the intended application, e.g. by mode coupling, dispersion and non-linear optical effects.
According to one embodiment example of the present invention, a laser weapon system is disclosed, which has at least one laser generating unit, at least one output stage element, a beam optics element, and a ground-based part and an air-based part, wherein the ground-based part is designed at least for generating energy for the laser weapon system, and the air-based part is configured for target acquisition and/or target tracking in the laser weapon system, wherein the beam optics element and the at least one output stage element are arranged on the fully movable part, characterized in that an optical fiber provides energy transmission from the ground-based part to the air-based part, and particularly provides a communications connection between ground-based part and air-based part.
According to the invention, the laser weapon system is divided into a static part, which is on a ground-based support (along with ancillary units) located on the ground, and a movable part (beam emitter) arranged on an airborne platform, wherein essentially all elements involving substantial mass and volume are preferably located in the static part, in order for the movable part that tracks the target to be as lightweight and agile as possible. The present invention therefore relates to a design for an airborne laser weapon system based on lasers pumped via optical waveguide.
This configuration is designed such that a system is produced in which the output beam, which is ultimately directed toward a target, can be focused within the fully encompassing half space, or at least in large portions thereof, wherein power is transmitted between the elements in which energy is converted from another energy form into optical radiant energy, and the final opto-mechanical element that is responsible for focusing the beam onto the target by means of fiber-optic elements. More particularly, the optical energy is not transmitted to the airborne platform via free beam guidance.
This can be accomplished by functionally dividing the beam source in such a way that, taking volume and mass into consideration, the components of the beam sources are separated into components that essentially codetermine mode quality and/or beam divergence, spectral properties and/or optical power.
In particular, an output stage that substantially determines the output beam quality, but which is responsible for only a fraction of the total volume and the total mass of a beam source may be coupled directly to a beam focusing unit, and may be situated on the airborne platform, while it continues to be supplied via fiber-optic elements with optical radiant power, which is generated in the pump sources which, together with the assigned ancillary units such as energy supply, cooling, etc., make up the majority of the total volume and the total mass of a beam source, wherein this second part may be arranged in a ground-based part of the system, and power and optical signals may be transmitted between these two parts via fiber-optic elements.
In this way, a tactical, airborne laser weapon system having relatively small dimensions, long sustainability and low costs can be provided, which is not significantly restricted in terms of its mobility and range, does not sacrifice the advantages of fiber-optic power transmission as opposed to free-beam transmission, such as robustness, reliability, independent adjustment, resistance to harsh environmental factors, flexible geometric design and low volume and mass etc., and does not require reductions in terms of mode quality and/or beam divergence, spectral properties or optical power, and therefore in the spectral radiation intensity that is available for a target, and therefore ultimately the effect that can be achieved. Moreover, operational reliability is thereby increased.
According to the invention, the beam emitter is supplied with radiant energy, i.e., the energy is transmitted from a ground-based carrier to the airborne platform by means of a towed optical waveguide. This allows optical radiant power in the high multi-kilowatt range to be transmitted over great distances of multiple kilometers. In so-called “laser drilling”, laser radiation for drilling into rock, e.g. for oil and gas prospection, may be used to heat the rock that will be bored to a high temperature, in order to decrease its mechanical strength and facilitate the subsequent conveyance by means of a drill string. In this process, the radiation of the laser may be guided via optical fiber to the head of the drill string, where it is used. However, in this case particularly, so-called multimode lasers and multimode optical waveguides may be used, with brilliance and beam quality being largely lost.
In the field of laser sources, in particular in the field of electrically pumped semiconductor lasers and/or diode lasers, solid-state laser sources and/or fiber lasers and the associated optics systems, it may be possible to generate, handle and focus optical power in the range of several kilowatts up to 100 kW or more with a high degree of efficiency, e.g., electrically/optically 25% or more. Such semiconductor and/or solid-state laser sources of maximum power and efficiency can preferably operate in the near infrared range (wavelength of approximately 800 nm to approximately 1.5 μm).
According to the invention, laser weapon systems based on high-powered lasers may be used against various classes of targets, for self-defense of platforms or for offensive missions. This includes missions against static targets, e.g. mines, barricades, fortifications and the like, but also against dynamic targets, e.g. as part of a defense against threats by flying objects (RAM—rocket, artillery, mortar), guided missiles with or without seeker heads, drones, UAVs, but also vehicles, weapon systems, radar systems, etc. To effectively oppose such targets, optical radiant power ranging from 10-100 kW or more may be provided. In this connection, it is in the general nature of a threat to arise without forewarning and from a previously unspecified direction, and to necessitate defensive action within periods of fractions of seconds up to several seconds.
It may therefore be necessary for an operational laser weapon system to be designed to enable operations against targets, and therefore to enable a beam focusing of the laser beam emitted by the system to be carried out with high spatial dynamics and precision. Typical acceptable values for focusing speeds and focusing accelerations are, e.g., 1 rad/s and 1 rad/s2, with a simultaneous final focusing precision of the emitted laser beam of 5 μrad. For such applications, the presence of large movable masses is avoided according to the invention.
To this extent, achieving suitable efficacy of a beam weapon system—in particular, a laser weapon system—against an object requires that the object—from the viewpoint of the system executing the effect—is located in the field of view of the system. Due to this specific precondition, which is determined by the substantially rectilinear propagation of the provided electromagnetic, optical or quasi-optical radiation, an object that is concealed, e.g., behind a geographic elevation, such as a mountain, or behind a house or a vehicle, cannot be easily impacted from a location near the ground. Notwithstanding the technical preconditions for implementation which are necessary when beam-type weapons are deployed over great distances due to the impact of the atmosphere on the radiation, the use of such systems on targets that are located beyond the horizon is possible only with great difficulty.
According to the invention, an action against a target object Z is not achieved directly from the location of the system that carries out the action; instead, an additional station is used as a relay point. In the concept of such a system, first an active laser beam of suitable power and other beam properties is generated by a base station B, and is then directed to a relay unit R located on an airborne platform and from this is either directed by passive deflection by means of a reflector to the target object, or is first received by a beam receiver, e.g. a receiving telescope, then focused and mode adjusted, in order to then be focused, following a suitable change in direction by a beam emitter, e.g. an emitting telescope, onto the target. In either case, it may be necessary for the relay station to be located on the airborne platform within the field of view of the base station, and for the target to be located within the field of view of the relay station on the airborne platform.
Both may be regularly ensured when the distance between the individual stations is not too great and the relay station is located at a sufficient elevation above the base line between the two other points B and Z, with the situation becoming more favorable as the elevation increases. However, at a great elevation, the resulting beam path as a whole along the distance from B to R to Z becomes increasingly larger. In contrast, a low elevation causes the angle of deflection between B to R and R to Z to become very shallow, making a passive deflection unfavorable due to the resulting sweeping incidence on the reflector. It is further noted that installing a high-powered laser on the ground and transmitting the generated laser radiation to the relay station via a free beam that is directed above the horizon is associated with certain safety risks. For instance, a beam that is not fully captured by the relay platform due to an error will continue to propagate in the original direction nearly without limits, and without substantial influence in terms of intensity, and will pass through the atmosphere and into space. There, it may present a hazard to air traffic and to satellites in perigee.
Another possible method for attacking a (ground) target from the air involves installing the entire laser system on board an airborne platform. For example, a high-powered laser of the 100 kW class, e.g. a chemical laser—COIL, may be installed on board a transport aircraft, and its generated radiation may be focused on a target by means of a beam focusing unit that projects out of the fuselage of the aircraft.
Regardless of the embodiment type of the actual laser-active medium (rod-, slab-, fiber- or disk laser) of a laser source, such a system can be implemented using a so-called diode pumped laser, e.g. designed as a solid-state laser, wherein liquid-, gas-, or metal vapor lasers may also be used, i.e., the primary energy in the form of electrical energy may be converted to radiant energy for the optical excitation of the laser-active medium using a (large) number of semiconductor lasers, diode lasers. A direct use of the radiation emitted by the semiconductor lasers may also be conceivable. In this case, the level of efficiency for the conversion of electrical energy to radiant energy for optical excitation, and for the conversion of this radiant energy for optical excitation to the optical output power of the laser system may be less than one due to the laws of physics. In general, efficiency levels of approximately 50% can be achieved for both processes, so that the total efficiency of the conversion of electrical energy to radiant energy of a laser, frequently referred to as the socket efficiency, can range from 25-50%, depending upon the type of embodiment. Additional optical losses may occur in the transmission of the radiant energy and electrical losses may occur in lines and in electronic circuits that are routinely used for the controlled manipulation of the semiconductor laser and for energy conversion.
According to the invention, in addition to these pump elements and the laser medium, a further plurality of functional elements, such as power supply, buffering, cooling, mechanical structure, optical elements, sensors and actuators, etc. are required for a functional laser weapon system.
The concept of the invention is characterized in that an airborne laser weapon system is produced in which all of the laser sources of the laser weapon system, or at least the parts thereof that are particularly bulky or heavy, such as pump sources, energy supply and storage, cooling, etc., together with the beam focusing unit, do not need to be carried along with the beam focusing unit on board the airborne platform. Moreover, the available operating duration is no longer subject to the narrow limits of an airborne platform when the energy supply is also carried along, and it is no longer necessary to guide a high-powered free beam that is subject to strict precision requirements through the atmosphere between two objects (ground station, relay) that are moving relative to one another and to a stationary reference system (ground), or to account for the fact that the fiber length that is required for beam transmission of the output power of the laser system with a towed fiber optic guide will negatively impact the properties of the beam. Moreover, the risk that is associated with a high-powered laser beam being emitted into open air space in the direction of the relay platform is naturally also eliminated. The solution according to the invention also results in a system with increased reliability and readiness for use, since the design of the system decreases the number of elements that are located on board the airborne platform and are subject there to the particular stresses of air transport, and is limited substantially to monolithic fiber elements.